The present invention concerns the field of handpieces for dental or surgical use. There are two families of handpieces: contra-angle handpieces which are equipped with an electrical motor and handpieces which include a turbine driven by compressed air.
We are concerned here with compressed air handpieces. In very simple terms, these compressed air handpieces include a head which houses a turbine. This turbine includes a compressed air feed pipe and a moving wheel provided with a plurality of regularly spaced blades at the periphery thereof. The feed pipe is used to force onto the turbine blades a compressed air flow whose pneumatic energy is converted into kinetic energy when the compressed air flow strikes the blades of the moving wheel.
FIG. 1 annexed to the present Patent Application is a perspective, cross-sectional view on a horizontal plane longitudinally intersecting the handle and the head of a compressed air handpiece according to the prior art. Designated as a whole by the general reference numeral 1, this handpiece includes a handle 2 which is connected to a head 4 which houses a turbine 6. Turbine 6 includes a moving wheel 8 from a periphery 10 of which extends a plurality of blades 12, which define an outer diameter 14 of moving wheel 8.
Handpiece 1 also includes injection means whose function is to direct onto blades 12 of moving wheel 8 a compressed air flow whose pneumatic energy is converted into kinetic energy when the compressed air flow strikes blades 12 of moving wheel 8. The compressed air injection means are formed of a compressed air feed pipe 16 which is machined in handle 2 of handpiece 1 using conventional techniques. Further, an air discharge pipe 18 is also machined by conventional techniques in handle 2 of handpiece 1, substantially parallel to and remote from compressed air feed pipe 16.
An examination of FIG. 1 reveals that compressed air feed pipe 16 is formed of a first and a second rectilinear pipe, respectively 20 and 22, arranged in the extension of each other, the longitudinal axis of symmetry 24 of second rectilinear pipe 22 extending slightly slantwise relative to longitudinal axis of symmetry 26 of handle 2 of handpiece 1 and making a non-zero angle a with the tangent 28 to outer diameter 14 of moving wheel 8. It is clear that it is difficult to envisage machining compressed air feed pipe 16 in a direction which would tend to move closer to the tangent 28 to outer diameter 14 of moving wheel 8 without risking piercing air discharge pipe 18 or having to reduce the diameter of pipe 18.
A recurrent problem facing designers of compressed air handpieces lies in the conversion efficiency between the pneumatic energy of the compressed air and the kinetic energy of the moving turbine wheel. Indeed, the mechanical power that the compressed air handpiece can deliver depends on this conversion efficiency. This conversion efficiency is closely connected, in particular, to the drop in pressure between the pressure of the compressed air which penetrates the head of the handpiece, and the pressure of the air leaving the head of the handpiece after the compressed air has struck the turbine blades. Indeed, the greater the pressure drop, the better the conversion between pneumatic energy and kinetic energy. The conversion efficiency between pneumatic energy and kinetic energy is also improved if the air flow occurs with minimal turbulence and thus minimal losses. It is also sought to reduce the operating noise of compressed air handpieces and to prevent, as far as possible, the compressed air intended to activate the turbine from escaping into the patient's mouth.